Abstract: A system may include a test chamber with an area to hold a sample of material (e.g., concrete, thermal backfill, or sand). The area may be subject to a variable desaturation vacuum to dry the sample. The test chamber may also have a precision scale to weigh the sample and a probe inside the sample to provide heat and measure temperature. A controller may automatically and repeatedly dry the sample by varying the desaturation vacuum. According to some embodiments, heat inside and/our outside the sample may also be applied to facilitate desaturation. The controller calculates a thermal resistivity based on heat input, temperature, and time data collected for different saturation levels. A test result data store may contain electronic records (with each record including thermal resistivity values over a range of moisture content values that represent a dryout curve for the material).